We report the instrumentation of a manufacturing composite process using an optical fiber sensor based on Bragg
gratings. The sensor is made of superimposed Long Period (LPG) and short period (FBG) Bragg gratings written in the
same fiber section. The monitoring of the process needs simultaneous measurements of temperature and strain. It has
been shown that these two solicitations can be determined and discriminated with a superimposed FBG/LPG sensor .
In this paper we present the device based on the dual superimposed gratings. The sensor is embedded in a composite
specimen manufactured by Vacuum Assisted Resin Transfer Moulding (VARTM) process for monitoring purpose.
We report here an optical sensor based on fiber Bragg gratings to measure strain and temperature effects simultaneously.
It has been shown that Long Period Grating (LPG) and Fiber Bragg Grating (FBG) exhibit different responses to an
applied solicitation, thus strain and temperature influences can be determined separately by measuring the corresponding
wavelength shifts [1,2]. In this paper we present a configuration based on the use of these two grating types: a LPG and a
FBG written in the same fiber section, which allows us to discriminate the contributions of these two main solicitations.
The sensor is embedded in a composite specimen manufactured by Liquid Resin Infusion (LRI) process for monitoring
We propose a framework for obtaining synthetic speckle-pattern images based on successive transformations of Perlin's coherent noise function. In addition we show how a given displacement function can be used to produce deformed images, making this framework suitable for performance analysis of speckle-based displacement/strain measurement techniques, such as Digital Image Correlation, widely used in experimental mechanics.
If a number of experiments aiming at demonstrating fundamental properties of phononic crystals have been successfully implemented, a need for enlarging both the research and the application fields of these structures has more recently risen. Surface acoustic waves appear as appealing candidates to set a new ground for illustrative experiments involving some different physical concepts from those usually observed when dealing with bulk waves. The possibility of a direct excitation of these surface waves on a piezoelectric material, and their already extensive use in ultrasonics also make them an interesting basis for phononic crystal based, acoustic signal processing devices. In this work, wave propagation in a square lattice, piezoelectric phononic crystal consisting of air holes etched in a lithium niobate matrix is both theoretically and experimentally investigated. The crystal was fabricated by reactive ion etching of a bulk lithium niobate substrate. Standard interdigital transducers were used to characterize the phononic structure by direct electrical generation and detection of surface waves. A full band gap around 200 MHz was experimentally demonstrated, and close agreement is found with theoretical predictions.
A Raman lidar dedicated to night-time tropospheric water-vapor high-resolution measurements is currently being developed at Réunion island in the south-western Indian Ocean. To our knowledge, it is the first permanent instrument of its kind in this tropical region. The geophysical and instrumental interests and issues on the radiative, dynamical and chemical plans for such a measurement, specially in the tropics, are obvious. The choice of a visible laser excitation wavelength was initially a constraint, in view of the weakness of the Raman scattering process that is the basis of the development of this instrument, but many arguments also plead for such a choice. After describing the water-vapor measurement method of this lidar, which is straightforward in principle, we stress on the main delicate underlying issues related to this method. A precise description of the optical parts of the lidar system is then given that emphasizes the importance of the rejection of the elastically backscattered signals in the Raman channels. Finally, we list the most important future works concerning the validation and calibration stages of this instrument that is intended to become an atmospheric surveillance instrument on a medium term.
The upper troposphere should play an important role on the climate. Several greenhouse gazes as well as cirrus clouds present in this region a large variability in both temporal and spatial scales. This variability is strongly connected with processes and air mass exchanges with the lower altitude as well as the stratosphere. The upper troposphere is not easy to probe nor from space nor from the ground. Lidar appears to be a good candidate for probing the upper troposphere. Ozone, water vapor, cirrus clouds, and temperature can be measure with lidar. All those measurements have been deployed in two sites. One is located in south of France at mid-latitude of the Northern Hemisphere and the other at the tropical site of the Southern Hemisphere: La Reunion. The technology has been improved to make such reliable measurements on a routine basis and to implement those measurements on a single lidar. Due to the episodic nature of the variability (in comparison with wave type variability), some questions about lidar signal integration need to be addressed. First climatologies of each parameter independently have been already obtained. Future strategy will be discussed.